Transporting substances, in particular fluids, over distance is required in many industries, this typically being achieved via a system of pipes, tubes, pipe modules, pipelines and the like. In the oil and gas exploration and production industry, for example, pipelines are used in many surface, subsurface and subsea environments to transport oil and/or gas, often over large distances.
In some instances, it may be necessary to isolate a section of a pipeline for repair or replacement. However, isolation of a section of pipe with piggable tools can be limited or prevented where a section of the pipe bore has a restriction or section of reduced inner diameter. This may be the case, for example, where a section of pipe is dented or otherwise damaged, thereby hindering or preventing deployment of isolation tooling through the pipe bore.
A number of solutions have been proposed for isolating sections of pipe where the pipe bore is restricted.
For example, local isolation can be achieved through the use of a hot tap inserted isolation tool such as the BISEP tool from STATS (UK) Limited. The BISEP offers double block and bleed isolation of a pipe through a single penetration in the pipe. Although hot tap inserted isolation tools offer an effective and economic solution for many applications, in some subsea applications it may be preferred to use remotely operated isolation tools or plugs, for example where access to the pipe is limited or not possible. Remotely operated isolation tools may also be preferred to minimise the vessel time and expense which may otherwise be necessary in transporting tooling to site.
Alternatively, a pigging isolation tool may be used, the pigging tool located within the pipe bore and propelled through the pipe by a pressure force generated by the pipe flow. In instances where restriction of the pipe bore is relatively small, a two plug train may be used having a high jump isolation plug (one with a large clearance to the pipe bore when deactivated), the tools being launched from one end of the pipe such that the front plug of the train passes the restriction/damaged section of pipe. The two plugs can then be set to isolate the restricted/damaged section of the pipe.
However, there is a limit to the radial jump (clearance between the plug body and the pipe bore) that can be accommodated by a double block and bleed mechanical isolation plug and in instances where restriction of the pipe bore is more substantial, use of a high jump isolation tool to pig past the bore restriction may not be feasible. For example, it is considered that current technology puts this limit at between about 5% and about 10% bore restriction dependant on pipe diameter.
For larger bore restrictions, and in particular those where the restriction is greater than 10% of the pipe bore, it may be desirable to pig tooling from both ends of the pipe and approach the restriction from both sides. However, in many situations this does not represent an effective solution. For example, in cases where there is no breach in the pipe, pigging from both ends may result in fluid in the pipe between the plugs being compressed, thereby raising the pipe pressure and risking damage to, or rupture of, the pipe or preventing pig movement.